12 replies to this topic

[Tarks]

hi, hope peeps can put some light to this, babybeks mpi cooper keeps deciding to slip its primary gear bush the rear larger diameter one!

its done it twice now why is this happening ?

to my knowledge the car is kept well on oil and its never given a hard time the gear seems well fitted to crank too.

has anyone had this issue either on road or race mini ? how can we solve it

as the bush slips over the holes the feel oil back behind the seal so it pushes down between the two bushes
and out all over the clutch and on the floor ! so a fooo bar gear and clutch again!

can anyone help ??

Edited by Tarks, 11 September 2006 - 05:59 PM.

[Bungle]

tarks is having problems with beks bush

[dklawson]

Very curious. The oil leak is as curious as the slipping. There are floating bushes for the primary gear and these have clearance between both the crankshaft and the ID of the primary gear. I'm not aware of any oil leak reports from people running the floating bush.

by the way, when you say the "rear" bush, the larger one, this doesn't make sense to me. The larger bush is the one closer to the block (1.625" ID) while the "rear" one is flanged and is closer to the C-clip on the crank tail. The flanged bushing should be 1.5" ID.

[Dan]

Have you fitted a new bush into a primary gear which has already had the bush slip inside it or is this a new primary gear?

[BabyBek]

HI there peeps!

DK - i'm not quite sure which one Tarks means!! I'll ask him and get back to you. As far as I recall its the one without the lip, but I could be mistaken!
We have a floating bush hanging around the garage somewhere I believe, I don't think we used it!.... again, I'll clarify with Tarks!

Dan - it was a rebushed 1ry (ie old gear, new bushes) BUT not the one that originally caused the problem.

P.S., I've just tried ringing Tarks but no answer!

[Tarks]

hello decorating in a new underground shopping mall no phone signal sorry bekx lol

yes dk rear larger lipless bush!

the floating bush we got was far too small in its I.D and would of needed to be lathed/machined to fit so i used another gear in perfect order but it seems to of happened again !

the bush isnt a solid one like the lipped one it is cut so it twists and moves over the oil way holes in the gear leaving no place for the oil to go other than out over crank onto clutch !

(i guess its poss we ordered the wrong floating bush from minisport but i dont know,
it looks like we need to get a new gear and bush, the type that circlips in place maybe it will cure the issues
can anyone help with a supplier of these?)
???????

Edited by Tarks, 12 September 2006 - 04:34 PM.

[dklawson]

I seem to remember that the small bore engines had different (smaller) primary gear bores but that may only apply to the early engines. Perhaps you have a floating bush for a small bore? Someone else will have to comment on small bore, early primary gears.

Any primary gear, press-in bushing has to be bored to size after installation. The dimensions I gave in my earlier post are the crank journal diameters. The notes I have call for an additional 0.004" clearance between the bushing and crank.

Partially related sidebar:
My 1275 is very early, one of the first 500. Its primary gear has a larger bore/seat for the bushings than later 1275s. I couldn't use the off-the-shelf one... it dropped into the primary gear with about 1/32" radial clearance. I had to make my own bushing.

I don't remember any spiral grooves in the primary gears I've seen. I'll have to look at the spare primary gear I have in the attic and look at it before I can comment about the oil holes.

[dklawson]

I checked my notes tonight. These are for early engines so you should check when and if this changed on later engines.

Early 850s and 1098s had both bushings in their primary gears bored to 1.378".
Early 998s had both bushings bored to 1.504".
Early 1275s had the flanged bushing bored to 1.504", the straight bushing bored 1.629".

I looked at the oil holes on my spare primary gear... which is from a later 1275 than mine. The holes are drilled at an angle between the oil seal area and an oil slinger ring adjacent to the helical gear teeth. If you're seeing a lot of oil pass through your primary gear into the clutch area, it might be that your crankcase doesn't have sufficient breathers. Perhaps pressure is building up and forcing oil through the flanged bushing. The leakage path for any such occurence would have to be through the little holes (and/or the large bush) then out through the flanged bushing.

The large bush should not cover the oil holes as you describe. The big bush is a press fit up against a shoulder (step) in the bore of the gear. The shoulder prevents the bush from covering the oil holes. I'm not sure what the twist is you're seeing but the bushing should be smooth, straight, and not cover the oil holes. This is also true of the floating bush, the shoulder in the gear limits its axial movement, preventing it from covering the oil holes. I have no idea what you mean about the bushes being held in by circlips. I've never seen this. The primary gears I've seen were all designed for press fit bushings.

[Tarks]

hi great notes cheers!

the twist is the actual bush movement! it seems to slip over the shoulder you mention thus covering some of the oil holes
and in turn leaving no where to go other than on the clutch through the radial clearence between gear and crank NEVER through the casing seal!


in theory it shouldnt be possible but twice now its happened

its an odd issue but other than lack of oil seizing the bush to the crank at high revs on motorway cardiff to leicester frequently and back,
or its high oil pressure but i would assume that wouldn't seize the gear bush,
no pickups on crank found last time im yet to take the car appart this timetho to have a look at crank id take a good guess the bush has slipped once again over the oil holes as before but we shall see on saturday.

[dklawson]

The bushing is a press fit so there should be absolutely no movement... unless you buy the floating bush.

The spinning / slipping won't happen on the highway. The only time the bushing slips on the crank is when you have the clutch pushed in. That's when things need to slip. At all times when you're moving and the clutch is engaged the bushing doesn't move relative to the crank.

Take a close look at the crank tail and carefully measure the crank and the bushing. The dimensions I gave above are for the bore in the bushing. The crank tail should measure about 0.004" under those figures where the bushings run.

Someone who has worked on the insides of more A-series engines than I needs to chime in. However, I don't believe that there is any pressurized oil fed to these bushings. That was done on the early 850s and proved to be a problem. The bushing type was changed and the drillings in the crank to feed the bushings were eliminated. Therefore, high oil pressure shouldn't cause this problem. The only way oil should be able to sneak out along this path is when there is excessive clearance crank-to-bushing. On most the primary gears I've seen, those little radial holes behind the seal area are partially or completely plugged with debris. IF your crankcase breathers are badly blocked or simply insufficient you could be building up pressure inside the engine and this could be causing or contributing to the problem. However, I'd expect you would be reporting oil dripping off the front timing cover and other places if this were happening.

[Tarks]

yes it seems that huge milage and low oil is an issue here as the seal on the timing chain cover has gone and it leaks oil id be tempted to change to the spring and ball type oil valve,
im going to replace the gear again this weekend ill check against your figures on its new fitment many thanks!

its only got to last till xmas, as jizz whizz has a body make over so engine will be on the work bench. ill go through it all again then, last year it was totally rebuilt but has covered over 25 thousand miles since so a new engine a tad aged already lol

but 07 will be a good year for jizz whizz, tlc on its way to make her a minter once again for beck x

THEN I MIGHT FIX HANOR MY VAN lol

[dklawson]

I don't want to beat a dead horse. I guess I'm not explaining something very well.

Leaks from the oil seals (clutch or pulley end) don't have to do with the oil pump. The crankcase builds up internal pressure just from the engine running. Oil is splashed all over the bottom end of the engine while it's running. Crankcase pressure can blow this splashed oil out of the engine when the oil lands near seals and such. You'll notice systems and hoses on the engine routed into the air intake system. Their intent is for moderate vacuum from the intake system to suck up some of the oil fumes and burn them. On the EARLY cars there was plenty of direct venting with a tube along the back side of the block directly to the atmosphere (and ground). As pollution laws became stricter it was necessary to find other ways to deal with oil fumes and the pressure in the crankcase. The PCV valves and additional vents are part of that. Even the oil filler cap on the valve cover is typically vented. This is a part that is seldom replaced, but it doesn't hurt to change it periodically. Your timing cover leak may be from old age and wear. On old engines with a lot of wear, blow-by from the pistons can make the crankcase pressure situation worse.

My point is, you may be chasing your tail trying to fix the primary gear if the real source of the problem is excessive pressure in the crankcase. You might find it helpful to start a new thread about crankcase vents and breathers and try some of the suggestions made before tearing everything apart to work on the primary gear again.

[Tarks]

im fully understanding you dk but i guess im not explaining properly

there is actual! movement of the bush the bush isnt a solid circle it has a cut down it so in terms if you got a bog roll and cut it once, then holding adjacent corners of the cut and pulled it you would end up with the result of what the bush in the engine has done

but yes as i mentioned i will look at oil pressure and breathers this weekend and ill have to replace gear again/bush as its damaged in this way again not that i would if it was at all poss to avoid.

ill take a picture of the gear and show my poor explanations in view

many thanks for all your help its given me routes to sources its cat of problems.

cheers